The present invention relates to a positive type resist composition which is sensitive to a radiation such as ultra violet ray, deep ultra violet ray, including eximer laser, electron beam, ion beam and X-rays, and is suitably used in producing semiconductor integrated circuits.
A lithography process using a resist composition has usually been adopted in a fine processing of semiconductor integrated circuit. Among the resist composition, positive working types are widely used because of their generally superior resolution. The positive resists contain generally an alkali-soluble ingredient and a radiation-sensitive ingredient. Specifically, novolak-quinonediazide type resists are known which contain a novolak resin as an alkali-soluble ingredient and a quinonediazide compound as a radiation-sensitive ingredient, and utilize the decomposition of the quinonediazide compound by the action of radiation to generate a carboxylic group, which changes the compound from alkali-insoluble to alkali-soluble.
In recent years, according to the demand for higher integration level, an integrated circuit having a finer circuit and a pattern formation at a sub-micron level has become required. As the result, a positive resist composition having a still higher resolution has become demanded. For satisfying this demand, so-called chemical amplification type resists, which utilize the chemical amplifying action of acid-generator, have also been used in some field. There is still, however, a persistent need for the novolak-quinonediazide resists.
The resolving power of the novolak-quinonediazide type positive resists may be improved by increasing the amount of the radiation-sensitive quinonediazide compound. However, there is a limitation, since the light absorption of the resist becomes so large that the profile is deteriorated and a rectangular pattern shape can not be obtained, when the amount of quinonediazide compound is too much. JP-A-61-141441 discloses an improvement in the sensitivity, heat resistance and others by adding an unesterified 2,3,4-trihydroxybenzophenone in addition to 1,2-naphthoquinonediazidesulfonic acid ester of 2,3,4-trihydroxybenzophenone which is a radiation-sensitive ingredient. Moreover, JP-A-1-289947, JP-A-2-2560, JP-A-3-191351 and others disclose an improvement in sensitivity, resolution and others by adding various polyhydric phenol compounds in addition to an alkali-soluble resin and a radiation-sensitive ingredient.
An object of the present invention is to further improve the resolution of the positive resists containing an alkali-soluble resin and a radiation-sensitive ingredient without deteriorating other resist performances. As the result of studies, the present inventors have found that the resolution of a positive resist composition which contains an alkali-soluble resin and a radiation-sensitive ingredient can be further improved by adding a certain compound. Thus, the present invention has been completed.